1. Field of the Invention
The present invention relates generally to media handling for high output printer. More particularly, the present invention relates to a method and apparatus for handling media, and therefore minimizing the downtime of the printer, preventing paper or media jams, and maximizing output.
2. Description of the Related Art
Inkjet printers typically include a media advancing assembly and a print head that repeatedly moves in a path that is transverse to the direction of the advancing media. After every pass of the print head, the media advances a distance equal to the width of a print swath. A microprocessor, which sends signals to a drive mechanism for a media feed roller, is used to control the direction and amount of media travel. In response to control signals from the processor, the feed roller rotates a predetermined amount. The feed roller and a set of pinch rollers pinches and feeds the media an amount desired for printing, cutting and/or other operations.
The carriage of the inkjet printer usually includes a set of print heads, with each print head representing a different color to be applied to the media, e.g. cyan, magenta, yellow, and black. To enable printing millions of colors, two or more of the nozzles may be directed to deposit ink at the same location on the media or the nozzles may be directed to deposit ink at a precise location with respect to deposits from other nozzles. Therefore, the accuracy of media advancement is of prime importance to the quality of the resulting printout. Under-advancement of the media will cause the print swaths to overlap, while over-advancement of the media will cause the print swaths to be separated.
Inkjet printers are particularly important for printing in color on labels because other color label printers are much more expensive. For example, the consumable materials that are required for a thermal color printer are much more expensive than the materials used in a color inkjet printer. Unfortunately, the performance of inkjet printers leaves much to be desired. A typical home or office inkjet printer is limited to a slow rate of printing because the printer is unable to feed media through itself at a high rate without causing media handling problems, such as media slippage.
These problems are well documented in the on-demand label/tag printing industry. In the label printing industry, the printing media is normally either in the form of a continuous roll or continuous folded stack of labels/tags. Prior to printing, the media from the roll or stack is typically fed through the printer until a forward edge of the media exits the feed roller at a position under the print head. In most instances, the pinch rollers must be released from the feed roller to ensure that the media can be loaded without obstruction. Once the media is loaded, the pinch rollers are lowered to thereby “pinch” or compress the media against the feed roller.
As is well known in the industry, printer operation is often interrupted when the printer runs out of paper, ink or toner, and needs to be re-supplied. A home or office user is generally able to tolerate the interruption and the resulting lower throughput. For example, if an office user needs to refill the printer with paper before completing, it is usually considered an inconsequential delay. This is because the utilization time of a home or office printer is not very high, i.e. the printer is often left idle. However, for applications such as the continuous mass printing of labels or tags where the utilization time of the printer is very high, delays to refill the printer with ink, paper, or media will dramatically lower throughput. Therefore, it is important to reduce not only the length of each interruption, but also the number of interruptions to the operation of a printer.
A further problem arises when the media is subjected to a series of interruptions or discontinuous start/stop cycles during printing. As the feed roller rotates through cycles of high acceleration and deceleration for every print swatch, the sudden pull of the media at the beginning of a cycle together with the back tension on the media may result in media slippage, particularly if the pinch pressure is insufficient. The issue of media slippage is even more pronounced with the much higher throughput requirements of inkjet printers designed for the high-speed printing industry in comparison to printers designed for typical home or office use. In addition, the greater inertia caused by using a large roll of media only exacerbates the slippage problem.
For example, in the high-speed label printing industry, it is highly advantageous to maximize the size of each individual roll of labels as well as to maximize the speed of the printing by pulling a sheet of labels from the roll through the printer as quickly as possible. The larger the roll that can be handled by the printer, the less the downtime suffered. Unfortunately, an increase in the size of the roll of media also increases the weight that must be pulled by the feed and pinch rollers. The increase in weight also increases the chances that the media will slip from one of the rollers and create a jam. In addition, each time the printer stops printing, the rollers must overcome great inertia to restart the printer and resume printing at a high speed. This is particularly true for inkjet printers, which are subject to more start/stop cycles than other printers.
Similar problems plague other media handling tasks that may interrupt the operation of the printer. These tasks include accommodating varying media dimensions and sizes, loading new media rolls (particularly in label printing applications), and guiding the media through the printer, (i.e. keeping the paper straight as it is being fed through the printer). Dealing with each case typically requires the printer to cease operation before the proper maintenance may be performed.
In view of the foregoing, it is desirable to have a method and apparatus providing for a high output inkjet printer. In particular, it is desirable to have a method and apparatus to handle and guide a large roll of media of varying dimensions and thickness through the high-speed printer with minimal slippage. In addition, it is desirable to be able to re-supply the printer with a new roll of media with minimal difficulty.